Method for modifying the water permeability of a subterranean formation

ABSTRACT

The invention relates to a method for modifying the water permeability of a subterranean formation, comprising at least the following steps:Preparing an injection fluid from a dispersion of a hydrophilic phase in a lipophilic phase, with water or brine, the dispersion comprising:a hydrophilic phase comprising at least one cross-linked (co)polymer PR,a lipophilic phase,at least one interface polymer composed of at least one monomer of formula (I):Injecting the injection fluid into the subterranean formation,said cross-linked (co)polymer PR forming a hydrogel in the presence of water.

FIELD OF THE INVENTION

This invention is in the field of recovering oil and gas from a subterranean formation. More particularly, the invention relates to a method for modifying the water permeability of a subterranean formation, comprising injecting, into the subterranean formation, an injection fluid comprising at least one (co)polymer encapsulated in a shell.

PRIOR ART

Injecting viscous or gelled polymer solutions into subterranean formations has been a very widespread practice for many years in order to improve hydrocarbon (oil and gas) recovery. These polymer solutions are used in particular to reduce or eliminate the water permeability of a zone or a part of a subterranean formation.

Formations sometimes have zones of interest containing hydrocarbons but with strong permeability contrasts or different water volume fractions. In such cases, and when additional pressure is applied in the subterranean formation with the injection of water in order to produce hydrocarbons, the injected water finds the path offering the least resistance to its propagation, namely the relative permeability most favourable to water, to reach the production wells rapidly; in other words, it passes through zones having a high volume fraction of water and/or having a high permeability, thus flowing past other zones rich in hydrocarbons that are less favourable to its propagation, without pushing them towards the production wells.

Polymer solutions are injected into such high-permeability and/or high water-content zones to replace the existing fluids and reduce their water permeability by virtue of their high viscosity. Once in their gelled form, these polymer solutions are used to divert the flow of water or gas towards the less permeable zones by permanently blocking the high-permeability zones. The blocking of certain zones may indeed prove necessary, since they may result in water inflows which seriously hinder hydrocarbon recovery.

However, during the injection of the polymers into the subterranean formation, the polymer solutions undergo mechanical and chemical degradation. Mechanical degradation is due to high shear stresses and elongational flows, especially in the initial injection unit, nozzles and pumps, constrictions in reservoirs and around wells. Chemical degradation is mainly due to the presence of oxygen, which is the most harmful factor with regard to the degradation of the polymer. The oxidative degradation of polymers is amplified by the presence of reducing chemical species such as iron and hydrogen sulphide. Thus, these different mechanisms lead to a partial degradation of the polymers and an inherent limitation to their effectiveness even before reaching the zone to be treated. These various degradations therefore require an overdose of polymer.

The treatment of subterranean formations often involves the use of cross-linking agents. These are added to the polymer solutions, as described in U.S. Pat. No. 4,683,949. The polymer/cross-linking agent mixture is then injected into the well to be treated with delayed gelation kinetics, the gel only setting after a few hours in the formation around the well. However, these methods are considered unreliable and often use products classified as hazardous to the environment, made from chromium salts or resins. Moreover, gel-based methods do not make it possible to easily control either the gelation kinetics or the consistency of the gel; they generate a high risk of damage to the well, cause the retention and adsorption of the cross-linking agent in the reservoir rock, and only allow the gel to be placed with difficulty in the high-permeability zones while preventing the oil or gas zones from being invaded due to, inter alia, the viscosity which they confer on the injected fluid.

The problem that the applicant proposes to solve is that of protecting, against chemical and mechanical degradation, the polymers used in a method for modifying the water permeability of a subterranean formation.

Disclosure of the Invention

The invention relates to a method for modifying the water permeability of a subterranean formation using a (co)polymer capable of forming a hydrogel in the presence of water. To this end, the (co)polymer is cross-linked. In the context of the present invention, the (co)polymer can be cross-linked at the latest in the subterranean formation in order to be able to modify the permeability of the latter. It is also possible to prepare a composition comprising a (co)polymer that is cross-linked prior to injecting the composition into the subterranean formation. The invention can therefore be implemented according to two different embodiments.

According to a first embodiment, the invention relates to a method for modifying the water permeability of a subterranean formation comprising at least the following steps:

-   -   Preparing an injection fluid from a dispersion of a hydrophilic         phase in a lipophilic phase, with water or brine, the dispersion         comprising:         -   a hydrophilic phase comprising at least one cross-linked             (co)polymer PR,         -   a lipophilic phase,         -   at least one interface polymer composed of at least one             monomer of formula (I):

-   -   -   in which,             -   R1, R2, R3 are independently selected from the group                 comprising a hydrogen atom, a methyl group and Z—X,             -   Z is selected from the group comprising C(═O)—O;                 C(═O)—NH; O—C(═O); NH—C(═O)—NH; NH—C(═O)—O; and a                 saturated or unsaturated, substituted or unsubstituted                 carbon chain having from 1 to 20 carbon atoms which may                 have one or more heteroatoms selected from nitrogen and                 oxygen,             -   X is a group chosen from the alkanolamides, sorbitan                 esters, ethoxylated sorbitan esters, glyceryl esters,                 and polyglycosides; and comprising a saturated or                 unsaturated, linear, branched or cyclic, optionally                 aromatic, hydrocarbon chain,         -   Injecting the injection fluid into a subterranean formation,             said cross-linked (co)polymer PR forming a hydrogel in the             presence of water.

According to a second embodiment, the invention relates to a method for modifying the water permeability of a subterranean formation comprising at least the following steps:

-   -   Preparing an injection fluid from a dispersion of a hydrophilic         phase in a lipophilic phase, with water or brine, the dispersion         comprising:         -   a hydrophilic phase comprising at least one non-cross-linked             (co)polymer NR,         -   a lipophilic phase,         -   at least one interface polymer composed of at least one             monomer of formula (I):

-   -   -   in which,             -   R1, R2, R3 are independently selected from the group                 comprising a hydrogen atom, a methyl group and Z—X,             -   Z is selected from the group comprising C(═O)—O;                 C(═O)—NH; O—C(═O); NH—C(═O)—NH; NH—C(═O)—O; and a                 saturated or unsaturated, substituted or unsubstituted                 carbon chain having from 1 to 20 carbon atoms which may                 have one or more heteroatoms selected from nitrogen and                 oxygen,             -   X is a group chosen from the alkanolamides, sorbitan                 esters, ethoxylated sorbitan esters, glyceryl esters,                 and polyglycosides; and comprising a saturated or                 unsaturated, linear, branched or cyclic, optionally                 aromatic, hydrocarbon chain,         -   Injecting the injection fluid and a cross-linking agent for             the (co)polymer NR into a subterranean formation,

    -   said (co)polymer NR, once cross-linked, forming a hydrogel in         the presence of water.

The expression “polymer composed of at least one monomer” means a polymer obtained from several molecules of at least one monomer. Thus, a polymer of one monomer corresponds to a polymer obtained from several repeating units of molecules of one monomer.

The Hydrophilic Phase in Lipophilic Phase Dispersion

The dispersion is a dispersion of a hydrophilic phase in a lipophilic phase. In other words, the lipophilic phase is the continuous phase and the hydrophilic phase is the dispersed phase. The interface polymer is positioned at the interface between the hydrophilic phase and the lipophilic phase. Preferably, the hydrophilic phase is an aqueous phase and the lipophilic phase is an oil phase. Thus, the composition of the invention is advantageously a water-in-oil dispersion, more advantageously a water-in-oil emulsion.

The interface polymer obtained by polymerization of at least one monomer of formula (I) forms a shell at the interface of the hydrophilic phase and the lipophilic phase. In general, the shell is resistant to mechanical stresses such as shearing and more particularly shearing when the polymer is dissolved, when it is injected through valves, chokes and other restrictions at passage speeds greater than 3 meters per second, or when flushing a subterranean formation in the vicinity of the reservoir/borehole interface. The shell is also resistant to chemical stresses which may result from the presence of oxygen, H₂S or metals during the injection phase. Preferentially, the shell is semi-permeable.

Preferably, as indicated above, the dispersion is basically in the form of an inverse emulsion.

In general, the hydrophilic phase is in the form of micrometric droplets dispersed, and advantageously emulsified, in the lipophilic phase. The average size of these droplets is advantageously between 0.01 and 30 μm, and more advantageously between 0.05 and 3 μm. The interface polymer is therefore positioned at the interface between the hydrophilic phase and the lipophilic phase at each droplet. The average size of the droplets is advantageously measured with a laser measuring apparatus using conventional techniques which are part of the general knowledge of a person skilled in the art. A Malvern Mastersizer device may be used for this purpose.

Generally, the dispersion according to the invention contains between 10 and 65% by weight of (co)polymer, and more advantageously between 30 and 60% by weight.

Moreover, the dispersion according to the invention has a hydrophilic phase/lipophilic phase weight ratio advantageously between 0.1 and 100, more advantageously between 1 and 80, and even more advantageously between 10 and 60.

The method for preparing the dispersion is described in the applicant's patent application FR 3 075 219, cited as a reference.

The (Co)Polymer PR or NR in the Hydrophilic Phase

The (co)polymer present in the hydrophilic phase may be a natural (co)polymer, such as, for example, xanthan gums, guar gums, schizophyllan, scleroglucan or other compounds of the polysaccharide family, or a synthetic or semi-synthetic (co)polymer. Preferably, the (co)polymer is a synthetic (co)polymer.

When the (co)polymer is a synthetic (co)polymer, it is preferably a (co)polymer obtained from at least one non-ionic monomer and/or at least one anionic monomer and/or at least one cationic monomer and/or a zwitterionic monomer.

The non-ionic monomer or monomers that may be used in the context of the invention may be chosen, in particular, from the group comprising water-soluble vinyl monomers. The non-ionic monomer does not comprise the monomers of formula (I). Preferred monomers belonging to this class are, for example, acrylamide, methacrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, and N-methylolacrylamide. Also, N-vinylformamide, N-vinylacetamide, N-vinylpyridine and N-vinylpyrrolidone, acryloyl morpholine (ACMO), glycidyl methacrylate, glyceryl methacrylate and diacetone acrylamide may be used. A preferred non-ionic monomer is acrylamide.

The anionic monomer or monomers are preferably selected from acrylic acid, methacrylic acid, itaconic acid, maleic acid, acrylamido tertiary butyl sulphonic acid (also called ATBS or 2-acrylamido-2-methylpropane sulphonic acid), vinylsulphonic acid, vinylphosphonic acid, said anionic monomer being unsalified, partially or totally salified, and salts of 3-sulphopropyl methacrylate. The salified form advantageously corresponds to the salts of alkali metals (Li, Na, K, etc.), alkaline earth metals (Ca, Mg, etc.) or ammonium, in particular quaternary ammonium.

Hereinbefore and below, cationic monomers and anionic monomers, such as, for example, DMAEMA and ATBS, include unsalified and partially or totally salified forms.

The cationic monomer or monomers that may be used in the context of the invention may be chosen, in particular, from monomers of the acrylamide, acrylic, vinyl, allylic or maleic type having a quaternary ammonium function by salification or quaternization. Mention may be made, in particular and in a non-limiting manner, of quaternized dimethylaminoethyl acrylate (DMAEA), quaternized dimethylaminoethyl methacrylate (DMAEMA), diallyldimethylammonium chloride (DADMAC), acrylamidopropyl trimethylammonium chloride (APTAC), and methacrylamido propyltrimethyl ammonium chloride (MAPTAC).

The cationic monomer or monomers may also be chosen from associative cationic monomers as described in patent FR 2 868 783.

The monomer may optionally be a zwitterionic monomer of the acrylamide, acrylic, vinyl, allylic or maleic type having a quaternary amine or ammonium function and a carboxylic, sulphonic or phosphoric acid function. Mention may be made, in particular and without limitation, of dimethylaminoethyl acrylate derivatives, such as 2-((2-(acryloyloxy)ethyl) dimethylammonio) ethane-1-sulphonate, 3-((2-(acryloyloxy)ethyl) dimethylammonio) propane-1-sulphonate, 4-((2-(acryloyloxy)ethyl) dimethylammonio) butane-1-sulphonate, [2-(acryloyloxy)ethyl] (dimethylammonio) acetate, dimethylaminoethyl methacrylate derivatives such as 2-((2-(methacryloyloxy) ethyl) dimethylammonio) ethane-1-sulphonate, 3-((2-(methacryloyloxy) ethyl) dimethylammonio) propane-1-sulphonate, 4-((2-(methacryloyloxy) ethyl) dimethylammonio) butane-1-sulphonate, [2-(methacryloyloxy)ethyl] (dimethylammonio) acetate, dimethylamino propylacrylamide derivatives such as 2-((3-acrylamidopropyl) dimethylammonio) ethane-1-sulphonate, 3-((3-acrylamidopropyl) dimethylammonio) propane-1-sulphonate, 4-((3-acrylamidopropyl) dimethylammonio) butane-1-sulphonate, [3-(acryloyloxy) propyl] dimethylammonio) acetate, dimethylamino propyl methylacrylamide derivatives, such as 2-((3-methacrylamidopropyl) dimethylammonio) ethane-1-sulphonate, 3-((3-methacrylamidopropyl) dimethylammonio) propane-1-sulphonate, 4-((3-methacrylamidopropyl) dimethylammonio) butane-1-sulphonate, and [3-(methacryloyloxy)propyl] (dimethylammonio) ethylammonio) acetate.

According to one particular embodiment of the invention, the (co)polymer is composed solely of ATBS.

The (co)polymer is preferably an anionic (co)polymer made from acrylamide, preferably an optionally partially post-hydrolyzed (co)polymer of acrylamide and acrylamido tertiary butyl sulphonic acid (ATBS), more preferably a ter(co)polymer of acrylamide, acrylic acid and acrylamido tertiary butyl sulphonic acid (ATBS).

The (co)polymer preferably contains between 10 mol % and 50 mol % of anionic monomer(s), and more preferably between 20 mol % and 45 mol %.

The (co)polymer preferably contains between 50 mol % and 90 mol % of non-ionic monomer(s), and more preferably between 60 mol % and 75 mol %.

Preferably, the (co)polymer contains only anionic and non-ionic monomer units. In other words, it is preferably obtained from at least one anionic monomer and at least one non-ionic monomer.

The (co)polymer may be obtained by any polymerization technique such as conventional radical polymerization, controlled radical polymerization, also referred to as RAFT (reversible-addition fragmentation chain transfer), NMP (nitroxide-mediated polymerization) or ATRP (atom transfer radical polymerization).

According to the first embodiment of the invention, the (co)polymer of the hydrophilic phase is cross-linked, PR. In this case, it is advantageously cross-linked by at least one cross-linking agent which may be chosen from the following groups:

-   -   polyethylenically unsaturated monomers (having at least two         unsaturated functions), such as, for example, vinyl, allyl,         acrylic and epoxy functions, for example         methylene-bis-acrylamide (MBA), triallyamine, or indeed, and/or     -   cross-linking agents made from multivalent metals such as salts         or complexes of Cr³⁺, Al³⁺, Fe³⁺ or Ti⁴⁺ and/or     -   macroinitiators such as polyperoxides, polyazos and transfer         polyagents such as polymercaptan (co)polymers, and polyols,         and/or     -   functionalized polysaccharides.

According to the first embodiment of the invention, the cross-linking leading to the (co)polymer PR is advantageously carried out during or after, and preferably during, the polymerization of the monomers.

According to the second embodiment of the invention, the cross-linking of the (co)polymer NR is not carried out in the dispersion. In this case, it is the (co)polymer NR. The (co)polymer NR, which is non-cross-linked, may be linear or branched. Preferably, the (co)polymer NR is linear. However, in order to carry out the invention, the (co)polymer NR is cross-linked once released directly into the injection fluid by means of at least one cross-linking agent which may be chosen from the above groups. This step is explained in greater detail below in the paragraph “Permeability modification method”.

The quantity of cross-linking agent in the (co)polymer NR or PR advantageously lies in the range from 0.1 ppm to 50,000 ppm by weight relative to the quantity of monomers, more advantageously in the range from 1 ppm to 5,000 ppm, and even more advantageously in the range from 10 ppm to 500 ppm.

Thus, this quantity of cross-linking agent is advantageously present in the injection fluid when the (co)polymer NR is used.

According to another particular embodiment of the invention, the (co)polymer of the hydrophilic phase (PR or NR) comprises at least one associative cationic monomer and/or at least one LCST group.

In accordance with a particular embodiment, the (co)polymer may comprise at least one LCST group.

According to the general knowledge of a person skilled in the art, an LCST group corresponds to a group whose solubility in water, for a given concentration, is modified above a certain temperature and depending on the salinity. It is a group having a heating transition temperature defining its lack of affinity with the solvent medium. Lack of affinity with the solvent results in opacification or loss of transparency which may be due to precipitation, aggregation, gelation or viscosification of the medium. The minimum transition temperature is referred to as the “LCST” (lower critical solution temperature). For each LCST group concentration, a heating transition temperature is observed. This is higher than the LCST, which is the minimum point of the curve. Below this temperature, the (co)polymer is soluble in water; above this temperature, the (co)polymer loses its solubility in water.

In accordance with a particular embodiment, the (co)polymer may comprise at least one UCST group.

According to the general knowledge of a person skilled in the art, a UCST group corresponds to a group whose solubility in water, for a given concentration, is modified below a certain temperature and depending on the salinity. It is a group having a cooling transition temperature defining its lack of affinity with the solvent medium. Lack of affinity with the solvent results in opacification or loss of transparency which may be due to precipitation, aggregation, gelation or viscosification of the medium. The maximum transition temperature is called “UCST” (upper critical solution temperature). For each UCST group concentration, a cooling transition temperature is observed. This is lower than the UCST, which is the maximum point of the curve. Above this temperature, the (co)polymer is soluble in water; below this temperature, the (co)polymer loses its solubility in water.

In accordance with the invention, the (co)polymer has an advantageously high molecular weight. The expression “high molecular weight” denotes molecular weights of at least 1 million g/mol, preferably between 2 and 40 million g/mol, and more preferably between 5 and 30 million g/mol. The molecular weight is understood as weight average molecular weight.

The Interface Polymer

As already indicated, the interface polymer is obtained from at least one monomer of formula (I):

-   -   in which,         -   R1, R2, R3 are independently selected from the group             comprising a hydrogen atom, a methyl group and Z—X,         -   Z is selected from the group comprising C(═O)—O; C(═O)—NH;             O—C(═O); NH—C(═O)—NH; NH—C(═O)—O; and a saturated or             unsaturated, substituted or unsubstituted carbon chain             having from 1 to 20 carbon atoms which may have one or more             heteroatoms selected from nitrogen and oxygen,         -   X is a group chosen from the alkanolamides, sorbitan esters,             ethoxylated sorbitan esters, glyceryl esters, and             polyglycosides; and comprising a saturated or unsaturated,             linear, branched or cyclic, optionally aromatic, hydrocarbon             chain.

In other words, X comprises a hydrocarbon chain and a group chosen from alkanolamides, sorbitan esters, ethoxylated sorbitan esters, glyceryl esters and polyglycosides. Advantageously, this hydrocarbon chain comprises C₂ to C₃₀ carbon atoms. In a preferred embodiment, it is an integral part of the group chosen from alkanolamides, sorbitan esters, ethoxylated sorbitan esters, glyceryl esters and polyglycosides.

X may therefore be one of the following groups:

-   -   an alkanolamide, preferably of the formula diethanolamide         monooleate (Witcamide 511), stearoyl ethanolamide (Witcamide         70), oleic acid monoisopropanolamide (Witcamide 61), isostearic         acid monoisopropanolamide (Witcamide SPA), coconut         monoisopropanolamide (Empilan CIS), coconut monoethanolamide,         oleic acid diethanolamide (Mexanyl), oleyl monoisopropanolamide         (Simaline IE 101),     -   a sorbitan ester, for example, but not limited to, sorbitan         monolaurate (Span 20), sorbitan monopalmitate (Span 40),         sorbitan monostearate (Span 60), sorbitan monoisostearate (Span         70), sorbitan tristearate (Span 65), sorbitan monooleate (Span         80), sorbitan sesquioleate (Span 83) or sorbitan trioleate (Span         85),     -   an ethoxylated sorbitan ester, preferably of the formula         polyethylene glycol sorbitan monolaurate (Tween 20),         polyethylene glycol sorbitan monopalmitate (Tween 40),         polyethylene glycol sorbitan monostearate (Tween 60),         polyethylene glycol sorbitan monooleate (Tween 80) or         polyethylene glycol sorbitan trioleate (Tween 85),     -   a glyceryl ester, preferably of the formula polyglycerol         monolaurate (Decaglyn 1-L), polyglycerol myristate (Decaglyn         1-M), polyglycerol decaoleate (Polyaldo 10-10-0), polyglycerol         distearate (Polyaldo 6-2-S), polyglycerol oleate (Polyaldo         10-1-0), polyglycerol caprate (Polyaldo 10-1 CC KFG), or         polyglycerol stearate (Polyaldo 10-1-S),     -   a polyglucoside, preferably of the formula decyl glucoside         (Triton BG-10), lauryl glucoside (Plantacare 1200UP), capryl         glucoside (Plantacare 810 UP), butyl glucoside (Simulsol SL 4),         heptyl glucoside (Simulsol SL 7 G), octyl and decyl glucoside         (Simulsol SL 8), decyl glucoside (Simulsol SL 10), undecyl         glucoside (Simulsol SL 11 W), decyl and hexadecyl glucoside         (Simulsol SL 26), or octyl and hexadecyl glucoside (Simulsol SL         826).

According to one particular embodiment, the monomer of formula (I) has an HLB value advantageously lower than 4.5, and advantageously of at least 1.

The HLB value (hydrophilic-lipophilic balance) makes it possible to quantify the balance that exists between the hydrophilic part and the lipophilic part of a molecule. This value is determined by calculating the values of the different parts of the molecule, as described by Griffin in 1949 (Griffin W C, Classification of Surface-Active Agents by HLB, Journal of the Society of Cosmetic Chemists 1 (1949): 311).

In the present invention, the Griffin method, conventionally used, is based on calculating the values of the chemical groups of the molecule. Griffin assigned a value of between 0 and 20, thus giving information on the solubility of the molecule in a hydrophilic medium and in a lipophilic medium. Thus, substances having an HLB of 10 are distributed equally in the two phases, i.e., the hydrophilic part in the hydrophilic phase and the hydrophobic part in the lipophilic phase.

HLB=20(Mh/M)

M: the molecular weight of the molecule

Mh: the molecular weight of the hydrophilic part.

In a preferred embodiment, the monomer of formula (I) has the following formula:

-   -   in which,         -   R1, R2, R3, independently, are a hydrogen atom or a methyl             group,         -   Z is selected from the group comprising CH₂, C(═O)—O,             C(═O)—NH, and —(C═O)—O—CH₂—CH(OH)—CH₂,     -   X is a group chosen from the alkanolamides and the sorbitan         esters, and comprising a saturated or unsaturated, linear,         branched or cyclic, optionally aromatic, hydrocarbon chain.

In accordance with a preferred embodiment, the monomer of formula (I) is selected from sorbitan monooleate (meth)acrylate, 2-hydroxypropyl (meth)acrylate of diethanolamide monooleate and sorbitan monooleate glyceryl (meth)acrylate.

In accordance with a preferred embodiment, the monomer of formula (I) is as follows:

This preferred monomer corresponds to the formula H₃C—(CH₂)₇—CH═CH—(CH₂)₇—C(═O)—N(CH₂CH₂OH)—(CH₂)₂—O—CH₂—CH(OH)—CH₂—O—C(═O)—C(CH₃)═CH₂.

In a particular embodiment of the invention, the interface polymer according to the invention is obtained by polymerization of at least one monomer of formula (I).

In a particular embodiment, the interface polymer according to the invention is obtained by polymerization of at least one monomer of formula (I) and at least one non-ionic monomer and/or at least one anionic monomer and/or at least one cationic monomer.

The various monomers that are implemented may be chosen from among the respective lists mentioned above in the description of the (co)polymer of the hydrophilic phase (PR or NR).

Advantageously, the interface polymer comprises between 0.0001 and 10%, more advantageously between 0.0001 and 5%, and even more advantageously between 0.0001 and 1% of the monomer of formula (I), by weight relative to the total weight of monomers.

In general, the time required to degrade the shell increases with the percentage of monomer of formula (I).

Where appropriate, the interface polymer comprises between 50 and 99.9999%, and more advantageously between 60 and 99.9999% of non-ionic monomer (different from the monomer of formula (I)) by weight relative to the total weight of monomers.

Where appropriate, the interface polymer comprises between 10 and 99.9999%, and more advantageously between 20 and 99.9999% of anionic monomer, by weight relative to the total weight of monomers.

Where appropriate, the interface polymer comprises between 1 and 99.9999%, and more advantageously between 10 and 99.9999% of cationic monomer, by weight relative to the total weight of monomers.

Advantageously, the interface polymer is neither cross-linked nor branched. It is advantageously linear.

The Shell

According to the invention, the interface polymer forms a shell around droplets forming the hydrophilic phase. In addition to the monomers mentioned above, the interface polymer may comprise at least one structural agent. The structural agent is advantageously chosen from diacrylamides or methacrylamides of diamines; acrylic esters of di-, tri- or tetrahydroxy compounds; methacrylic esters of di-, tri- or tetrahydroxy compounds; divinyl compounds preferably separated by an azo group; diallyl compounds preferably separated by an azo group; vinyl esters of di- or trifunctional acids; allyl esters of di- or trifunctional acids; methylenebisacrylamide; diallylamine; triallylamine; tetraallylammonium chloride; divinylsulphone; polyethylene glycol dimethacrylate and diethylene glycol diallyl ether.

Permeability Modification Method

The injection fluid used in the method according to the invention has the functionality of gelling in high-permeability and/or high water-content zones in order to reduce or eliminate the permeability of these zones.

Whatever the form used (a dispersion, a concentrated dispersion or a solid form obtained from the dispersion), the protective effect of the shell is produced and the (co)polymers PR and NR are thus protected from chemical and mechanical degradation, in particular during injection.

In other words, and more precisely, the method for modifying the water permeability of a subterranean formation according to the invention comprises the following steps:

-   -   Preparing an aqueous injection fluid by adding, to water or         brine, the dispersion a hydrophilic phase in a lipophilic phase         as described above, or its concentrated form after removal of         part of the water, or its solid form obtained after drying of         said dispersion,     -   Injecting the injection fluid into a subterranean formation,     -   Releasing said (co)polymer PR or NR by hydrolysis of the         interface polymer,     -   Modifying the water permeability of the subterranean formation         by gelation of said injection fluid.

The operations of modifying the water permeability of a reservoir differ from enhanced oil recovery techniques. The modification operations are characterized by volume-limited injections of polymer solution in order to create a localized phenomenon in the reservoir, namely, for conformance, blocking of the high-permeability zones and, for stopping water, blocking of zones where water enters the formation. Injections are generally carried out either via an injection well or via a production well over fairly short periods of a few days and generally less than one month, and with volumes representing less than 5% of the pore volume of the reservoir. The pore volume corresponds to the volume not occupied by rock in the reservoir, which allows a correlation with the permeable zone.

Conversely, polymer-based enhanced oil recovery techniques involve the continuous and prolonged injection of polymer solution to flush the reservoir from an injection well to a production well. The objective is not to treat a zone of the reservoir but the reservoir as a whole, in order to recover the maximum amount of oil. For this purpose, it is necessary to inject a much larger volume of aqueous solution generally representing at least 50% to 500%, or even more, of the pore volume. An oily and sometimes gaseous aqueous mixture is then recovered from the production wells.

As already indicated, the (co)polymer PR is in cross-linked form in order to be able to modify the permeability of the subterranean formation, the (co)polymer PR forming a hydrogel in the presence of water. In other words, when it is released from the shell, the (co)polymer PR swells by taking up water. By swelling, the (co)polymer PR causes the injection fluid to gel, thereby forming a hydrogel. The gelation of the injection fluid results in the blocking of certain zones and consequently the modification of the permeability of the subterranean formation.

As already indicated, the (co)polymer NR is not in cross-linked form when the injection fluid is injected. Once released from the shell, the (co)polymer NR cross-links, with the aid of a cross-linking agent, forming a hydrogel in the presence of water. In other words, when it is in cross-linked form, the (co)polymer NR swells by taking up water. By swelling, the cross-linked (co)polymer NR causes the injection fluid to gel, thereby forming a hydrogel. The gelation of the injection fluid results in the blocking of certain zones and consequently the modification of the permeability of the subterranean formation.

As previously mentioned, the dispersion as described above makes it possible not only to protect the (co)polymers PR and NR from chemical and mechanical degradation during the steps of preparing and injecting the injection fluid, but also to delay the gelation of the fluid. These properties are obtained by virtue of the shell formed by the interface polymer which, when degraded by hydrolysis, leads to the release of the (co)polymer PR or NR.

According to the second embodiment of the invention, in which the (co)polymer NR is subjected to a cross-linking step after its release from the dispersion, the injection fluid comprises at least one cross-linking agent which can be chosen from the cross-linking agents mentioned above, in particular cross-linking agents made from multivalent metals such as salts or complexes of Cr³⁺, Al³⁺, Fe³⁺ or Ti⁴⁺. In this particular embodiment, once the (co)polymer has been released, it reacts with the cross-linking agent present in the injection fluid to form a gel. According to this embodiment, the (co)polymer of the hydrophilic phase is generally not cross-linked before it is released.

In a particular embodiment of the first embodiment of the invention, a cross-linking agent as described above can also be injected with the injection fluid even if the (co)polymer PR is already cross-linked. Indeed, depending on the characteristics of the subterranean formation, it may be advantageous to cross-link the (co)polymer PR more strongly.

According to the invention (PR or NR, depending on the embodiment), the injection fluid advantageously comprises between 30 ppm and 50,000 ppm (by weight) of the dispersion or concentrated dispersion or solid form obtained from the dispersion, more advantageously between 100 and 30,000 ppm, and even more advantageously between 300 and 15,000 ppm.

According to the invention, the injection fluid advantageously comprises between 10 ppm and 15,000 ppm (by weight) of (co)polymer (PR or NR according to the embodiment), more advantageously between 50 and 10,000 ppm, and even more advantageously between 100 and 5,000 ppm.

Once the injection fluid is injected, the (co)polymer is released following degradation of the shell formed by the interface polymer under the temperature and/or pH conditions of the subterranean formation.

Thus, the (co)polymer included in the hydrophilic phase is protected by the shell formed from at least one interface polymer obtained by polymerization of at least one monomer of formula (I), the shell being capable of being degraded under the temperature and/or pH conditions of the subterranean formation.

The method according to the invention makes it possible to protect the polymer from mechanical and chemical degradation (oxygen, metals, H₂S) linked to the preparation of the composition injected with the polymer, and to its injection, while maintaining good injectivity and a good ability to block the permeable zones of the subterranean formation. In addition, the shell makes it possible to delay the release of the (co)polymers.

Without wishing to be bound to any theory, the formation of the injection fluid by introducing the dispersion according to the invention does not make it possible to release the (co)polymer from its shell, even in the presence of a reverser (oil-in-water surfactant). The pH and/or temperature of the subterranean formation allows hydrolysis of the interface polymer and thus the delayed release of the (co)polymer.

The invention and the advantages resulting from it appear more clearly from the following figures and examples that are given to illustrate the invention and in non-limiting manner.

DESCRIPTION OF THE FIGURES EXAMPLES OF EMBODIMENTS OF THE INVENTION Example 1

Part A: Preparation of a Composition C1 comprising a Monomer X1 Corresponding to Formula (I)

0.16 g of glycidyl methacrylate (97% by weight aqueous solution) is added to 20.0 g of oleyl diethanolamide (diethanolamide monooleate Witcamide 511-AkzoNobel) with magnetic stirring. The medium is stirred for 12 hours at ambient temperature.

Part B: Preparation of a Dispersion with an Interface Polymer (Invention)

A hydrophilic phase is prepared containing 365.8 g of acrylamide (50% by weight aqueous solution), 24.6 g of acrylic acid (100%), 234.6 g of sodium salt of 2-acrylamido-2-tert-butylsulphonic acid (50% by weight aqueous solution), 29.0 g of deionized water, 25.9 g of sodium hydroxide (50% by weight aqueous solution), 0.5 g of methylenebisacrylamide, 1.6 g of an aqueous solution of sodium hypophosphite (5 g/L), 0.94 g of tert-butyl hydroperoxide (0.7% by weight aqueous solution), 0.40 g of pentasodium salt of diethylenetriaminepentaacetic acid (Versenex 80) dispersed in a mixture of 280 g of aliphatic hydrocarbon D100S (Exxsol D100) and 20 g of composition Cl comprising a monomer X1 of part A. The pH is adjusted to 6.50.

After homogenization and deoxygenation with nitrogen for 30 minutes, polymerization is initiated by adding a sodium bisulphite solution.

Example 2

Part A: Preparation of a Composition C2 Comprising a Monomer X2 Corresponding to Formula (I)

15.7 g of glycidyl methacrylate (97% by weight aqueous solution) is added dropwise to 20.0 g of oleyl diethanolamide (diethanolamide monooleate Witcamide 511-AkzoNobel) with magnetic stirring. The medium is stirred for 12 hours at ambient temperature.

Part B: Preparation of a Dispersion without Interface Polymer (Counter-Example)

A hydrophilic phase is prepared containing 365.8 g of acrylamide (50% by weight aqueous solution), 24.6 g of acrylic acid (100%), 234.6 g of sodium salt of 2-acrylamido-2-tert-butylsulphonic acid (50% by weight aqueous solution), 29.0 g of deionized water, 25.9 g of sodium hydroxide (50% by weight aqueous solution), 0.5 g of methylenebisacrylamide, 1.6 g of an aqueous solution of sodium hypophosphite (5 g/L), 0.94 g of tert-butyl hydroperoxide (0.7% by weight aqueous solution), 0.40 g of pentasodium salt of diethylenetriaminepentaacetic acid (Versenex 80) dispersed in a mixture of 280 g of aliphatic hydrocarbon D100S (Exxsol D100) and 20 g of oleyl diethanolamide (diethanolamide monooleate Witcamide 511-AkzoNobel). The pH is adjusted to 6.50.

After homogenization and deoxygenation with nitrogen for 30 minutes, polymerization is initiated by adding a sodium bisulphite solution.

Part C: Preparation of a Dispersion with an Interface Polymer from a Dispersion without an Interface Polymer (Invention)

36 g of acrylamide (50% by weight aqueous solution), 1.6 g of tert-butyl hydroperoxide (0.7% by weight aqueous solution) and 0.6 g of composition C2 comprising a monomer X2 are added to the dispersion obtained in part B. The formation of the interface polymer, by polymerization of the monomers of composition C2, is initiated by adding a sodium bisulphite solution (radical initiator).

Resistance to Mechanical Degradation

In order to demonstrate the mechanical protection of the polymer provided by the shell, aqueous solutions containing 1000 ppm of the polymer of example 1 (with shell) and of the counter-example (without shell—example 2, part B) were prepared in synthetic seawater. The solutions were sheared by passing them through a pipe with a small cross-section at different pressures. The shear gradient was determined by measuring the flow at the outlet of a 0.5 mm capillary. The samples were then collected at the outlet of the pipe and the viscosity was measured at 7.3 s⁻¹ and 25° C. on a Kinexus pro+ by Malvern Instruments.

The data is displayed in Table 1. The polymer with no shell is rapidly degraded. Polymer solutions that have a shell maintain constant viscosities very close to 1.0 cp (1 cp=1 cps=1 mPa·s). The solutions prepared according to the invention were collected after shearing, i.e., at each measurement point. After measuring their viscosity, they were then activated by being placed for 4 days in an oven at 60° C. Their viscosity after the release of the water-soluble polymer was then measured. The latter remains very close to the viscosity of the non-sheared solutions without an initial shell (counter-example).

TABLE 1 Viscosity (cp) of the polymer solution measured at 7.3 s⁻¹ and T = 25° C. as a function of the previously applied shear. Shear gradient (s⁻¹) 0 50,000 100,000 148,000 210,000 Counter-example: 8.1 6.5 5.1 4.2 3.3 viscosity without shell Example 1: 1.1 1.0 1.0 1.0 1.0 viscosity with shell Example 1: 8.0 8.1 8.1 7.9 8.0 viscosity after degradation of the shell 

1. A method for modifying water permeability of a subterranean formation, comprising at least the following steps: preparing an injection fluid from a dispersion of a hydrophilic phase in a lipophilic phase, with water or brine, the dispersion comprising: a hydrophilic phase comprising at least one cross-linked (co)polymer PR, a lipophilic phase, at least one interface polymer composed of at least one monomer of formula (I):

in which, R1, R2, R3 are independently selected from the group consisting of a hydrogen atom, a methyl group and Z—X, Z is selected from the group consisting of C(═O)—O; C(═O)—NH; O—C(═O); NH—C(═O)—NH; NH—C(═O)—O; and a saturated or unsaturated, substituted or unsubstituted carbon chain having from 1 to 20 carbon atoms which may have one or more heteroatoms selected from nitrogen and oxygen, X is a group chosen from alkanolamides, sorbitan esters, ethoxylated sorbitan esters, glyceryl esters, and polyglycosides; and comprising a saturated or unsaturated, linear, branched or cyclic, optionally aromatic, hydrocarbon chain, injecting the injection fluid into the subterranean formation, said cross-linked (co)polymer PR forming a hydrogel in the presence of water.
 2. The method for modifying the water permeability of a subterranean formation, comprising at least the following steps: preparing an injection fluid from a dispersion of a hydrophilic phase in a lipophilic phase, with water or brine, the dispersion comprising: a hydrophilic phase comprising at least one non-cross-linked (co)polymer NR, a lipophilic phase, at least one interface polymer composed of at least one monomer of formula (I):

in which, R1, R2, R3 are independently selected from the group consisting of a hydrogen atom, a methyl group and Z—X, Z is selected from the group consisting of C(═O)—O; C(═O)—NH; O—C(═O); NH—C(═O)—NH; NH—C(═O)—O; and a saturated or unsaturated, substituted or unsubstituted carbon chain having from 1 to 20 carbon atoms which may have one or more heteroatoms selected from nitrogen and oxygen, X is a group chosen from the alkanolamides, sorbitan esters, ethoxylated sorbitan esters, glyceryl esters, and polyglycosides; and comprising a saturated or unsaturated, linear, branched or cyclic, optionally aromatic, hydrocarbon chain, injecting the injection fluid and a cross-linking agent for the (co)polymer NR into a subterranean formation, said (co)polymer NR, once cross-linked, forming a hydrogel in the presence of water.
 3. The method according to claim 1, wherein the (co)polymer PR or NR is obtained from at least one non-ionic monomer and/or at least one anionic monomer and/or at least one cationic monomer and/or at least one zwitterionic monomer.
 4. The method according to claim 3, wherein the non-ionic monomer is selected from the group consisting of acrylamide, methacrylamide, N-i sopropylacrylamide, N,N-dimethylacrylamide, N-methylol acrylamide, N-vinylformamide, N-vinylacetamide, N-vinylpyridine, N-vinylpyrrolidone, acryloyl morpholine, glycidyl methacrylate, glyceryl methacrylate and diacetone acrylamide.
 5. The method according to claim 3, wherein the anionic monomer is chosen from the group consisting of salts of 3-sulphopropyl methacrylate, and unsalified, partially or totally salified monomers chosen from acrylic acid, methacrylic acid, itaconic acid, maleic acid, acrylamido tertiary butyl sulphonic acid, vinylsulphonic acid, and vinylphosphonic acid.
 6. The method according to claim 1, wherein the interface polymer comprises, in addition to the monomer of formula (I), at least one non-ionic monomer and/or at least one anionic monomer and/or at least one cationic monomer.
 7. The method according to claim 1, wherein the monomer of formula (I) has the following formula:

in which, R1, R2, R3, independently, are a hydrogen atom or a methyl group, Z is selected from the group consisting of CH₂, C(═O)—O, C(═O)—NH, and —(C═O)—O—CH₂—CH(OH)—CH₂, X is a group chosen from alkanolamides and sorbitan esters, and comprising a saturated or unsaturated, linear, branched or cyclic, optionally aromatic, hydrocarbon chain.
 8. The method according to claim 1, wherein the monomer of formula (I) is selected from sorbitan monooleate (meth)acrylate, 2-hydroxypropyl (meth)acrylate of diethanolamide monooleate or sorbitan monooleate glyceryl (meth)acrylate.
 9. The method according to claim 1, characterized in that the monomer of formula (I) has the following formula:


10. The method according to claim 1, wherein the (co)polymer comprises at least one associative cationic monomer and/or at least one LCST group.
 11. The method according to claim 1, wherein the injection fluid comprises at least one cross-linking agent.
 12. The method according to claim 2, wherein the (co)polymer PR or NR is obtained from at least one non-ionic monomer and/or at least one anionic monomer and/or at least one cationic monomer and/or at least one zwitterionic monomer.
 13. The method according to claim 12, wherein the non-ionic monomer is selected from the group consisting of acrylamide, methacrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, N-methylolacrylamide, N-vinylformamide, N-vinyl acetamide, N-vinylpyridine, N-vinylpyrrolidone, acryloyl morpholine, glycidyl methacrylate, glyceryl methacrylate and diacetone acrylamide.
 14. The method according to claim 13, wherein the anionic monomer is chosen from the group consisting of salts of 3-sulphopropyl methacrylate, and unsalified, partially or totally salified monomers chosen from acrylic acid, methacrylic acid, itaconic acid, maleic acid, acrylamido tertiary butyl sulphonic acid, vinylsulphonic acid, and vinylphosphonic acid.
 15. The method according to claim 14, wherein the interface polymer comprises, in addition to the monomer of formula (I), at least one non-ionic monomer and/or at least one anionic monomer and/or at least one cationic monomer.
 16. The method according to claim 15, wherein the monomer of formula (I) has the following formula:

in which, R1, R2, R3, independently, are a hydrogen atom or a methyl group, Z is selected from the group consisting of CH₂, C(═O)—O, C(═O)—NH, and —(C═O)—O—CH₂—CH(OH)—CH₂, X is a group chosen from alkanolamides and sorbitan esters, and comprising a saturated or unsaturated, linear, branched or cyclic, optionally aromatic, hydrocarbon chain.
 17. The method according to claim 2, wherein the monomer of formula (I) is selected from sorbitan monooleate (meth)acrylate, 2-hydroxypropyl (meth)acrylate of diethanolamide monooleate or sorbitan monooleate glyceryl (meth)acrylate.
 18. The method according to claim 3, wherein the monomer of formula (I) is selected from sorbitan monooleate (meth)acrylate, 2-hydroxypropyl (meth)acrylate of diethanolamide monooleate or sorbitan monooleate glyceryl (meth)acrylate.
 19. The method according to claim 9, wherein the (co)polymer PR or NR is obtained from at least one non-ionic monomer and/or at least one anionic monomer and/or at least one cationic monomer and/or at least one zwitterionic monomer, and wherein: the non-ionic monomer is selected from the group consisting of acrylamide, methacrylamide, N-i sopropylacrylamide, N,N-dimethylacrylamide, N-methylol acrylamide, N-vinylformamide, N-vinylacetamide, N-vinylpyridine, N-vinylpyrrolidone, acryloyl morpholine, glycidyl methacrylate, glyceryl methacrylate and diacetone acrylamide; and the anionic monomer is chosen from the group consisting of salts of 3-sulphopropyl methacrylate, and unsalified, partially or totally salified monomers chosen from acrylic acid, methacrylic acid, itaconic acid, maleic acid, acrylamido tertiary butyl sulphonic acid, vinylsulphonic acid, and vinylphosphonic acid.
 20. The method according to claim 19, wherein the (co)polymer comprises at least one associative cationic monomer and/or at least one LCST group. 